1. Field of the Invention
The present invention relates to a plasma display panel (also referred to as “PDP”) and a plasma display device.
2. Description of the Background Art
FIG. 23 is a perspective view illustrating a PDP 51P including a discharge inert film, which is disclosed in Japanese Patent Application Laid Open Gazette No. 9-102280. The discharge inert film is also reffered to as a “discharge deactivation film”, as a “discharge passivation film” or as a “discharge inhibiting film”. The PDP 51P of FIG. 23 is a surface discharge type AC-PDP. The PDP 51P is broadly divided into a front substrate 51FP, a rear (or back) substrate 51R, and a barrier rib 7 and a phosphor 8 which are disposed between the front substrate 51FP and the rear substrate 51R.
The front substrate 51FP includes a front glass substrate 5, a plurality of sustain discharge electrodes X and Y, a dielectric layer 3, a cathode film 11 and a discharge inert film 21P. In more detail, a plurality of sustain discharge electrodes X and Y are alternately arranged on a main surface of the front glass substrate 5 along a first direction D1 and extend along a second direction D2 which intersects (herein, orthogonal to) the first direction D1. Adjacent two of the alternate sustain discharge electrodes X and Y make a pair, and a pair of two sustain discharge electrodes (hereinafter, referred to also as “sustain discharge electrode pair”) X and Y are arranged with a discharge gap portion DG interposed therebetween. A portion between the adjacent pairs of sustain discharge electrodes X and Y is hereafter referred to as “adjoining sustain discharge electrode pair gap portion” (or “electrode pair gap portion”) NG.
The pair of sustain discharge electrodes X and Y define a display line L extending along the second direction D2, and the display line L is schematically indicated by an alternate long and short dash line (or chain line) in FIG. 23, which is present between the pair of sustain discharge electrodes X and Y or in the discharge gap portion DG. In this case, the discharge gap portions DG extending along the second direction D2 correspond to the display lines L, respectively.
Each of the sustain discharge electrodes X and Y is constituted of a transparent electrode 1 and a bus electrode 2. Specifically, the transparent electrode 1 extends along the second direction D2. The transparent electrodes 1 of a pair of sustain discharge electrodes X and Y are arranged with the discharge gap portion DG interposed therebetween. The bus electrode 2 extends along the second direction D2 on each transparent electrode 1. The bus electrode 2 is disposed on a side farther away from the discharge gap portion DG. The bus electrode 2 is mainly made of a metal, serving to supply a voltage to the transparent electrode 1. In the sustain discharge electrodes X and Y, a portion of the transparent electrode 1 on which the bus electrode 2 is not present is referred to as “transparent portion” and a portion of the transparent electrode 1 on which the bus electrode 2 is present, in other words, a portion other than the transparent portion is referred to as “metal electrode portion”.
The dielectric layer 3 and the cathode film 11 are formed on the main surface of the front glass substrate 5 in this order, covering the sustain discharge electrodes X and Y. The cathode film 11 is formed by vapor deposition of MgO.
In the PDP 51P, the discharge inert film 21P is formed on the cathode film 11. Specifically, the discharge inert film 21P has a plurality of strip-like patterns, being in a stripe shape. Each strip-like pattern of the discharge inert film 21P is disposed on adjacent two bus electrodes 2 (which are adjacent to each other but belong to different pairs of sustain discharge electrodes X and Y) provided between adjacent display lines L, and between the two bus electrodes 2 as (the main surface of the front substrate 51FP or the front glass substrate 5 is) two-dimensionally viewed. In other words, each strip-like pattern of the discharge inert film 21P is disposed on the metal electrode portions of the not-paired adjacent sustain discharge electrodes X and Y and the electrode pair gap portion NG between the metal electrode portions as two-dimensionally viewed.
Thus, since the discharge inert film 21P is formed on the cathode film 11, exposed surfaces 11S of the cathode film 11 and exposed surfaces 21SP of the discharge inert film 21P are disposed in an upper portion of the dielectric layer 3. In this case, each exposed surface 11S is formed in an area corresponding to the display line L due to the patterns of the discharge inert film 21P.
On the other hand, the rear substrate 51R includes a rear glass substrate 9, a plurality of address electrodes 6 (or W) and an overglaze layer 10. In more detail, a plurality of address electrodes 6 (or W) are arranged on a main surface of the rear glass substrate 9 along the second direction D2, extending along the first direction D1, i.e., a direction that (grade-separately or three-dimensionally) intersects the sustain discharge electrodes X and Y. The overglaze layer 10 is formed on the main surface of the rear glass substrate 9, covering the address electrodes 6.
Further, the barrier rib 7 is disposed on the overglaze layer 10. Specifically, the barrier rib 7 has a plurality of strip-like patterns, being in a stripe shape. Each strip-like pattern of the barrier rib 7 is disposed between adjacent two address electrodes 6 along the first direction D1 as (the main surface of the rear substrate 51R or the rear glass substrate 9 is) two-dimensionally viewed. On inner surfaces of a plurality of U-shaped trenches each constituted of the barrier rib 7 and the overglaze layer 10, the phosphors 8 are formed. In each U-shaped trench, the phosphor 8R, 8G or 8B which emits light of red, green or blue, respectively, is disposed.
The front substrate 51FP and the rear substrate 51R are layered in a third direction D3 which intersects (herein, orthogonal to) both the first direction D1 and the second direction D2 with a top of the barrier rib 7 and the discharge inert film 21P abutting on each other, and sealed at their rim. In this case, a plurality of discharge spaces 51S are formed in the PDP 51P, being sectioned mainly by the barrier ribs 7, more specifically, surrounded by the phosphors 8, the cathode film 11 and the discharge inert film 21P. The discharge space 51S is filled with a mixed gas such as Ne+Xe. The discharge space 51S is opposed to the address electrode 6, extending along the first direction D1.
In the PDP 51P, a grade-separated intersection between the sustain discharge electrode pair X and Y and the address electrode 6 (or W) or a grade-separated intersection between the discharge space 51S and the display line L, which is a crossing point as two-dimensionally viewed, corresponds to one discharge cell (hereinafter, also referred to simply as “cell”). In other words, a plurality of discharge cells are arranged on each display line L and a display area of the PDP 51P is formed of a plurality of discharge cells arranged in matrix on the whole.
The discharge inert film 21P is mainly made of a material having work function larger than MgO which is a material of the cathode film 11, in other words, emitting less secondary electrons than the cathode film 11, such as A12O3 or TiO2. Therefore, even if the sustain discharge electrodes X and Y are present below the discharge inert film 21P, a discharge is hard to generate above the discharge inert film 21P. On the other hand, the exposed surface 11S of the cathode film 11 which is made of MgO having better secondary electron emission characteristic than the discharge inert film 21P is exposed to the discharge space 51S above the discharge gap portion DG and the transparent portions of the sustain discharge electrodes X and Y Therefore, as shown in FIG. 23, a surface discharge 50 generated between the paired sustain discharge electrodes X and Y is limited in an area where no discharge inert film 21P is present. This produces the following effects (1), (2) and (3).
(1) Since a formation area or the size of the surface discharge 50 between the paired sustain discharge electrodes X and Y can be reduced by increasing the area of the exposed surfaces 21SP of the discharge inert film 21P, it is possible to suppress discharge currents. This allows reduction of load of an external circuit to drive the sustain discharge electrodes X and Y, and a circuit cost can be thereby lowered.
(2) If no discharge inert film 21P is present, the surface discharge 50 between the paired sustain discharge electrodes X and Y extends up to above the bus electrode 2. At such a time, part of visible lights emitted from the phosphor 8 by an ultraviolet ray in generation of surface discharge 50 is blocked by the bus electrode 2 and not used as a display light. On the other hand, in the PDP 51P, since the surface discharge 50 is distributed only above the transparent portion where no bus electrode 2 is present, it is possible to reduce the ratio of blocked visible lights from the phosphor 8 to be blocked. This increases luminous efficiency.
(3) The surface discharges 50 on adjacent display lines L are separated by (the strip-like patterns of) the discharge inert film 21P more certainly. Therefore, it is possible to suppress a wrong discharge between the adjacent display lines L even if the electrode pair gap portion NG is narrowed. This is advantageous in achieving densely formation of the display lines L and higher definition of a display.
The discharge inert film which is so disposed as to mainly cover an area corresponding to the area between the adjacent display lines is disclosed in Japanese Patent Application Laid Open Gazette Nos. 10-255664, 10-333636, 2000-39866, 2000-100337, 2000-156166, 2001-147660 and 2001-176400 besides the above-discussed Japanese Patent Application Laid Open Gazette No. 9-102280.
The discharge inert film 21P is patterned by a vapor deposition lift-off method which is disclosed in the above Japanese Patent Application Laid Open Gazette Nos. 9-102280 and 2000-39866. In the patterning of the vapor deposition lift-off method, a resist (having a shape of inverted pattern of the discharge inert film 21P) is formed on a surface of the cathode film 11 by photolithography, a discharge inert material is so vapor-deposited as to cover the resist and finally the resist is lifted off. The vapor deposition lift-off method, which is based on the photolithography, has excellent accuracy in size and shape of the discharge inert film 21P and patterning position of the discharge inert film 21P relative to the pattern of the sustain discharge electrodes X and Y. Therefore, the above effects (1), (2) and (3) can be produced certainly also in a quantitative respect. Since costly processes of photolithography, vapor deposition and lift-off are executed, however, the vapor deposition lift-off method itself disadvantageously requires high cost.
Further, as another method of patterning the discharge inert film, a thick film paste containing a discharge inert material such as Al2O3 is applied directly on the cathode film by a screen printing method or the like and fired (or burned).
The Japanese Patent Application Laid Open Gazette No. 2000-156166, for example, discloses a method in which a protection film having low ratio of secondary electron emission, or the discharge inert material, which covers a surface of MgO above the adjoining sustain discharge electrode pair gap portion and does not cover above the sustain discharge electrodes, is formed of a dielectric glass containing a specific material such as Al2O3 by screen printing and firing.
Next, a method of driving the PDP 51P will be discussed, referring to FIGS. 24 and 25. Some of the methods of driving the surface discharge type AC-PDP including the discharge inert film 21P formed on the cathode film 11 are disclosed in Japanese Patent Application Laid Open Gazette Nos. 10-333636, 2000-39866 and 2001-147660.
FIG. 24 is a conceptual diagram showing an exemplary field division of screen in displaying a color image of 256-level gray scale. In this case, one screen (main frame) is constituted of 8 subfields SF (the first subfield SF1 to the eighth subfield SF8), and each subfield SF consists of a reset period REP, a writing period AD and a discharge sustain period SU. The discharge sustain period SU of each subfield SF is ranked (weighted), and specifically, the length of the discharge sustain period SU in the (N+1)-th subfield is almost twice as long as that of the N-th subfield, where N is a natural number.
In a cell selected by application of a pulse-like voltage to its address electrode 6 during the writing period AD of each subfield, sustain discharges as much as the applied sustain pulses are generated during the discharge sustain period SU. Since the number of sustain pulses is almost proportional to the length of the discharge sustain period SU, the luminescence intensity of the cell selected during the writing period AD is almost doubled as the subfield SF advances by one. At this time, by combination of light emission and no light emission in the subfields SF1 to SF8 (in other words, selection and non-selection of the subfields SF1 to SF8), it is possible to control the luminescence intensity of 28=256 levels. In other words, a display of 256-level gray scale can be achieved in one main frame.
FIG. 25 is a timing chart (for one subfield SF) used for explaining a method of driving the PDP 51P in the background art. In the driving method, the reset period REP consists of the first, second and third reset periods RE1, RE2P and RE3. In the first reset period RE1, a first priming pulse is given to all the discharge cells by applying a pulse P1 having a writing potential Vw to all the address electrodes W. In the subsequent second reset period RE2P, a second priming pulse is given to all the discharge cells by applying a pulse P2 having the writing potential Vw to all the address electrodes W and applying a pulse P3P having a potential Vxh to all the sustain discharge electrodes X. With the first and second priming pulses, priming discharges for stabilizing the following operation are generated between the paired sustain discharge electrodes X and Y in all the discharge cells. After that, in the third reset period RE3, wall charges are initialized in all the discharge cells by applying an erase pulse to the sustain discharge electrodes X and Y. FIG. 25 shows a case where a narrow erase pulse P4 is applied as the erase pulse to the sustain discharge electrodes X. Potentials Vxm and Vym of FIG. 25 are intermediate potentials and a potential Vyb is a scanbase potential.
Subsequently, in the writing period AD, n (n is a natural number) sustain discharge electrodes Y (Y1 to Yn) are sequentially switched to sequentially select (scan) the display lines L and an image signal indicating selection/non-selection of the corresponding cell is applied to each address electrode W in synchronization with this sequential selection (scan). Thus, a writing discharge is generated in the sustain discharge electrode pair X and Y of the selected cell and the wall charges are accumulated therein.
Next, in the discharge sustain period SU, a sustain pulse is alternatingly applied predetermined times to the sustain discharge electrodes X and Y. With this application, in the cell selected in the preceding writing period AD, a predetermined number of sustain discharges are generated by synergism of the sustain pulse and the wall charges. On the other hand, in the cell not selected in the writing period AD, which does not have sufficient wall charge which is needed to start the sustain discharge, no sustain discharge is generated. Thus, a desired image can be obtained.
The technique relevant to a PDP is shown in e.g., the following patent documents 1 to 21 and non-patent documents 1 to 5. Further, the patent document 3 corresponds to the patent document 2, the patent document 5 corresponds to the patent document 4, and the patent document 15 corresponds to the patent document 14.    (Patent Document 1) Japanese Patent Application Laid Open Gazette No. 9-102280,    (Patent Document 2) Japanese Patent Application Laid Open Gazette No. 10-255664,    (Patent Document 3) U.S. Pat. No. 6,137,226,    (Patent Document 4) Japanese Patent Application Laid Open Gazette No. 10-333636,    (Patent Document 5) U.S. Pat. No. 6,031,329,    (Patent Document 6) Japanese Patent Application Laid Open Gazette No. 2000-39866,    (Patent Document 7) Japanese Patent Application Laid Open Gazette No. 2001-147660,    (Patent Document 8) Japanese Patent Application Laid Open Gazette No. 2002-56775,    (Patent Document 9) Japanese Patent Application Laid Open Gazette No. 10-149774,    (Patent Document 10) Japanese Patent Application Laid Open Gazette No. 2001-160361,    (Patent Document 11) Japanese Patent Application Laid Open Gazette No. 2000-100337,    (Patent Document 12) Japanese Patent Application Laid Open Gazette No. 2000-156166,    (Patent Document 13) Japanese Patent Application Laid Open Gazette No. 2001-176400,    (Patent Document 14) Japanese Patent Application Laid Open Gazette No. 2000-113828,    (Patent Document 15) EP No. 993017 A1,    (Patent Document 16) Japanese Patent Application Laid Open Gazette No. 9-237580,    (Patent Document 17) Japanese Patent Application Laid Open Gazette No. 2000-195431,    (Patent Document 18) Japanese Patent Application Laid Open Gazette No. 2000-311612,    (Patent Document 19) Japanese Patent Application Laid Open Gazette No. 10-233171,    (Patent Document 20) Japanese Patent Application Laid Open Gazette No. 2001-183999,    (Patent Document 21) Japanese Patent Application Laid Open Gazette No. 2001-15034,    (Patent Document 22) Japanese Patent Application Laid Open Gazette No. 11-149873, and    (Patent Document 23) Japanese Patent Application Laid Open Gazette No. 2002-83545.    (Non-Patent Document 1) Kimio Amemiya, Toshihiro Komaki, Takashi Nishio, High Luminous Efficiency and High Definition Coplanar AC-PDP with “T”-shaped Electrodes, “Proceedings of the 5th International Display Workshops (IDW '98)”. pp. 531-534.    (Non-Patent Document 2) Y. Hashimoto, Y. Seo, O. Toyoda, K. Betsui, T. Kosaka, and F. Namiki, High-Luminance and Highly Luminous-Efficient AC-PDP with DelTA Cell Structure, “Society for Information Display 2001 (SID 01) DIGEST”, pp. 1328-1331.    (Non-Patent Document 3) Y. Tanaka, H. Honma, H. Hasegawa, N. Aibara, T. Nakamura, A new progressive driving scheme for a PDP with “CASTLE” structure, “Proceedings of The 21st International Display Research Conference in conjunction with The 8th International Display Workshops (Asia Display/IDW '01)”, pp. 869-872.    (Non-Patent Document 4) H. Hirakawa, T. Shiizaki, H. Nakahara, Y. Kawanami, M. Tajima, An Advanced Progressive Driving Method for PDP with Horizontal Barrier Ribs and Common Electrodes. “Proceedings of The 21st International Display Research Conference in conjunction with The 8th International Display Workshops (Asia Display/IDW '01)”, pp. 1757-1758.    (Non-Patent Document 5) T. Komaki, H. Taniguchi, K. Amemiya, High Luminance AC-PDPs with Waffle-structured Barrier Ribs, “Proceedings of the 6th International Display Workshops (IDW '99)”, pp. 587-590.    (Non-Patent Document 6) Jae-Young Lee, Min-Nung Hur, Yun-Gi Kim, Jae-Hwa Ryu, Jung-Soo Cho, Chung-Hoo Park, A Study on the New Shaped Align-Free Sustain Electrodes Showing High Luminous Efficiency in AC PDPs, “Proceedings of The 7th International Display Workshops (IDW '00)”, pp. 623-626.
As discussed above, in the Japanese Patent Application Laid Open Gazette No. 2000-156166 disclosed is the method of forming the discharge inert film of a dielectric glass containing a specific material such as Al2O3 by screen printing and firing. When the inventor of the present invention, however, tries to form a discharge inert film, as the discharge inert film 21P of the PDP 51P, of a dielectric glass whose main material is TiO2 or Al2O3 by screen printing, with a thickness of several μm, it is found that the minimum sustain pulse voltage required for a sustain discharge between the paired sustain discharge electrodes X and Y (usually, about 150 V) becomes higher than usual by about 100 V and a practical driving is difficult. Moreover, even when the discharge inert film is formed by the same method in part of the adjoining sustain discharge electrode pair gap portion away from a formation area of the surface discharge between the sustain discharge electrodes X and Y by a predetermined distance without covering the upper portions of the sustain discharge electrodes X and Y, the same result is obtained.
It is further found from the examination by the inventor of the present invention that applying the driving method of FIG. 25 to the PDP 51P including the discharge inert film 21P formed by the above-discussed vapor deposition lift-off method causes a problem that sustain discharge is not generated well enough during the discharge sustain period SU even in the cell selected in the writing period AD.